Fibrous Network Structure Having Excellent Compression Durability

ABSTRACT

The present invention provides a network structure having excellent repeated compression durability, the network structure having a low repeated compression residual strain and a high hardness retention after repeated compression. 
     A network structure comprising a three-dimensional random loop bonded structure obtained by forming random loops with curling treatment of a continuous linear structure including a polyester-based thermoplastic elastomer and having a fineness of not less than 100 dtex and not more than 60000 dtex, and by making each loop mutually contact in a molten state, wherein the network structure has an apparent density of 0.005 g/cm 3  to 0.20 g/cm 3 , a 50%-constant displacement repeated compression residual strain of not more than 15%, and a 50%-compression hardness retention of not less than 85% after 50%-constant displacement repeated compression.

TECHNICAL FIELD

The present invention relates to a network structure suitable forcushioning materials that are used for office chairs, furniture, sofas,beddings such as beds, and seats for vehicles such as those for trains,automobiles, two-wheeled vehicles, buggies and child seats, and floormats and mats for impact absorption such as members for prevention ofcollision and nipping, etc., the network structure having excellentrepeated compression durability.

BACKGROUND ART

At present, foamed-crosslinking type urethanes are widely used acushioning material that is used for furniture, beddings such as beds,and seats for vehicles such as those for trains, automobiles andtwo-wheeled vehicles.

Although foamed-crosslinking type urethanes have excellent durability asa cushioning material, they have inferior moisture and waterpermeability and air permeability, and have thermal storage property toexhibit possible humid feeling. Since the foamed-crosslinking typeurethanes do not have thermoplasticity, they have difficulty inrecycling, and therefore they give significant damage to incinerators incase of incineration, and need high costs in elimination of poisonousgas. For this reason, the foamed-crosslinking type urethanes are oftendisposed of by landfill, but limitation of landfill spots based ondifficulty of stabilization of ground causes problems of the necessityfor higher costs. Furthermore, although the foamed-crosslinking typeurethanes have excellent workability, they may cause various problemssuch as pollution problems with chemicals that have been used in themanufacturing process, residual chemicals after foaming and associatedoffensive odors.

Patent Documents 1 and 2 disclose network structures. They are capableof solving various problems associated with the foamed-crosslinking typeurethanes and have excellent cushioning performance. As for repeatedcompression durability properties, however, although performance withregard to the repeated compression residual strain is excellent for the20000-times repeated compression residual strain being not more than20%, a hardness after repeated use is low for the 50%-compressionhardness retention after repeated compression being only about 83%.

Foamed-crosslinking type urethanes have been heretofore considered tohave sufficient durability performance if the repeated compressionresidual strain is low. In recent years, however, it has beenincreasingly required to secure cushioning performance after repeateduse with compression as requirements for repeated compression durabilityhave become higher. However, in regard to the conventional networkstructures, it is difficult to obtain a network structure havingdurability performance which satisfies both the requirements of lowrepeated compression residual strain and high hardness retention afterrepeated compression.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Publication No. H7-68061A-   Patent Document 2: Japanese Patent Publication No. 2004-244740A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been completed in consideration of theproblems of conventional technology described above, and aims atproviding a network structure having excellent repeated compressiondurability, the network structure having a low repeated compressionresidual strain and a high hardness retention after repeatedcompression.

Means for Solving the Problems

The present invention has been completed as result of wholeheartedinvestigation performed by the present inventors in order to solve theabove-described problems. That is, the present invention includes:

1. A network structure comprising a three-dimensional random loop bondedstructure obtained by forming random loops with curling treatment of acontinuous linear structure including a polyester-based thermoplasticelastomer and having a fineness of not less than 100 dtex and not morethan 60000 dtex, and by making each loop mutually contact in a moltenstate, wherein the network structure has an apparent density of 0.005g/cm³ to 0.20 g/cm³, a 50%-constant displacement repeated compressionresidual strain of not more than 15%, and a 50%-compression hardnessretention of not less than 85% after 50%-constant displacement repeatedcompression.

2. The network structure according to the above 1, wherein the networkstructure has a 25%-compression hardness retention of not less than 85%after 50%-constant displacement repeated compression.

3. The network structure according to the above 1 or 2, wherein thenetwork structure has a thickness of not less than 10 mm and not morethan 300 mm.

4. The network structure according to any one of the above 1 to 3,wherein the cross section of the continuous linear structure that formsthe network structure is a hollow cross section and/or a modified crosssection.

5. The network structure according to any one of the above 1 to 4,wherein the network structure has a hysteresis loss of not more than28%.

6. The network structure according to any one of the above 1 to 5,wherein the network structure has a number of bonding points per unitweight of 60/g to 500/g.

Effect of the Invention

A network structure according to the present invention is a networkstructure having excellent repeated compression durability, the networkstructure having a low repeated compression residual strain and highhardness retention after repeated compression and hardly causing achange in sitting comfort and sleeping comfort even after repeated use.The excellent repeated compression durability has made it possible toprovide a network structure suitable for cushioning materials that areused for office chairs, furniture, sofas, beddings such as beds, andseats for vehicles such as those for trains, automobiles, two-wheeledvehicles, buggies and child seats, and floor mats and mats for impactabsorption such as members for prevention of collision and nipping, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic graph of a compression/decompression testin the hysteresis loss measurement of a network structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The network structure of the present invention is a network structuremade of a three-dimensional random loop bonded structure obtained byforming random loops with curling treatment of a continuous linearstructure including a polyester-based thermoplastic elastomer and havinga fineness of not less than 100 dtex and not more than 60000 dtex, andby making each loop mutually contact in a molten state, wherein thenetwork structure has an apparent density of 0.005 g/cm³ to 0.20 g/cm³,a 50%-constant displacement repeated compression residual strain of notmore than 15%, and a 50%-compression hardness retention of not less than85% after 50%-constant displacement repeated compression.

As the polyester-based thermoplastic elastomer in the present invention,a polyester ether block copolymer having a thermoplastic polyester as ahard segment and a polyalkylenediol as a soft segment or a polyesterester block copolymer having an aliphatic polyester as a soft segmentmay be mentioned as examples.

The polyester ether block copolymer is a triblock copolymer formed of atleast one of dicarboxylic acids selected from aromatic dicarboxylicacids such as terephthalic acid, isophthalic acid,naphthalene-2,6-dicarboxylic acid, naphthalane-2,7-dicarboxylic acid anddiphenyl-4,4′-dicarboxylic acid, cycloaliphatic dicarboxylic acids suchas 1,4-cyclohexanedicarboxylic acid, aliphatic dicarboxylic acids suchas succinic acid, adipic acid, sebacic acid and dimer acid and esterforming derivatives thereof, at least one of diol components selectedfrom aliphatic diols such as 1,4-butanediol, ethylene glycol,trimethylene glycol, tetramethylene glycol, pentamethylene glycol andhexamethylene glycol and cycloaliphatic diols such as1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and ester formingderivatives thereof; and at least one of polyalkylenediols such asglycols including polyethylene glycol, polypropylene glycol,polytetramethylene glycol or an ethylene oxide-propylene oxidecopolymer, the number average molecular weight of which is about 300 to5000.

The polyester ester block copolymer is a triblock copolymer formed of atleast one of the above-described dicarboxylic acids, at least one of theabove-described diols, and at least one of polyester diols such aspolylactone, the number average molecular weight of which is about 300to 5000. When considering heat adhesiveness, hydrolysis resistance,stretchability and heat resistance etc., triblock copolymers havingterephthalic acid or naphthalene-2,6-dicarboxylic acid as a dicarboxylicacid, 1,4-butanediol as a diol component, and polytetramethylene glycolas a polyalkylenediol, or triblock copolymers having polylactone as apolyester diol are especially preferred. In special cases, thosecontaining a polysiloxane-based soft segment may also be used.

The polyester-based thermoplastic elastomer in the present inventionalso encompasses those obtained by blending or copolymerizing anon-elastomer component with the polyester-based thermoplastic elastomerand those having a polyolefin-based component as a soft segment.Further, those obtained by adding various kinds of additives etc. to thepolyester-based thermoplastic elastomer as necessary are alsoencompassed.

For achieving repeated compression durability of a network structure,which is an object of the present invention, the content of a softsegment in the polyester-based thermoplastic elastomer is preferably notless than 15% by weight, more preferably not less than 25% by weight,still more preferably not less than 30% by weight, especially preferablynot less than 40% by weight, and for securing the hardness and from theviewpoint of heat and setting resistance, the content of a soft segmentin the polyester-based thermoplastic elastomer is preferably not morethan 80% by weight, more preferably not more than 70% by weight.

Preferably, a component including the polyester-based thermoplasticelastomer, which forms the network structure having excellent repeatedcompression durability of the present invention, has an endothermic peakat a temperature of not higher than the melting point in a melting curveobtained by measurement using a differential scanning calorimeter. Thosehaving an endothermic peak at a temperature of not higher than themelting point have significantly improved heat and setting resistance ascompared to those having no endothermic peak. For example, when, as thepreferred polyester-based thermoplastic elastomer in the presentinvention, an acid component of hard segment containing terephthalicacid or naphthalene-2,6-dicarboxylic acid etc. having stiffness in anamount of not less than 90% by mol, the content of terephthalic acid ornaphthalene-2,6-dicarboxylic acid being more preferably not less than95% by mol, especially preferably 100% by mol, and a glycol componentare subjected to transesterification, the resulting product is thenpolymerized to a necessary polymerization degree, and not less than 15%by weight and not more than 80% by weight, more preferably not less than25% by weight and not more than 70% by weight, still more preferably notless than 30% by weight and not more than 70% by weight, especiallypreferably not less than 40% by weight and not more than 70% by weightof polytetramethylene glycol having an average molecular weight of notless than 500 and not more than 5000, more preferably not less than 700and not more than 3000, still more preferably not less than 800 and notmore than 1800 is then copolymerized, crystallinity of hard segment isimproved, plastic deformation is hard to occur and heat and settingresistance is improved when the acid component of hard segment has ahigh content of terephthalic acid and naphthalene-2,6-dicarboxylic acidhaving stiffness. When annealing treatment is further performed at atemperature lower by at least 10° C. than the melting point afterhot-melt bonding, heat and setting resistance is further improved. Itsuffices that the sample can be heat-treated at a temperature lower byat least 10° C. than the melting point in annealing treatment, but heatand setting resistance is further improved when a compressive strain isimparted. An endothermic peak appears more clearly at a temperature ofnot lower than room temperature and not higher than the melting point ina melting curve obtained by measuring the cushioning layer treated asdescribed above using a differential scanning calorimeter. Whenannealing is not performed, an endothermic peak does not appear clearlyin the melting curve at a temperature of not lower than room temperatureand not higher than the melting point. From this, it can be thought thatby annealing, a hard segment is rearranged to form a semi-stableintermediate phase, so that heat and setting resistance is improved. Asan approach for utilizing the heat resistance improving effect in thepresent invention, use in applications supposed to involve a relativelyhigh temperature, such as cushions for vehicles using a heater andflooring mats for heated floors, is effective because setting resistanceis improved in those applications.

The fineness of the continuous linear structure which forms the networkstructure of the present invention should be set in a proper rangebecause when the fineness is small, a necessary hardness cannot bemaintained when the network structure is used as a cushioning material,and conversely when the fineness is excessively large, the hardnessbecomes excessively high. The fineness is not less than 100 dtex,preferably not less than 300 dtex. When the fineness is less than 100dtex, the network structure becomes so thin that although denseness andsoft touch are improved, it is difficult to secure a necessary hardnessas a network structure. The fineness is not more than 60000 dtex,preferably not more than 50000 dtex. When the fineness is more than60000, the hardness of the network structure can be sufficientlysecured, but the network structure may become coarse, leading todeterioration of other cushioning performance.

The apparent density of the network structure of the present inventionis 0.005 g/cm³ to 0.20 g/cm³, preferably 0.01 g/cm³ to 0.18 g/cm³, morepreferably 0.02 g/cm³ to 0.15 g/cm³. When the apparent density issmaller than 0.005 g/cm³, a necessary hardness cannot be maintained whenthe network structure is used as a cushioning material, and converselywhen the apparent density is more than 0.20 g/cm³, the hardness maybecome so high that the network structure is unsuitable for a cushioningmaterial.

The thickness of the network structure of the present invention ispreferably not less than 10 mm, more preferably not less than 20 mm.When the thickness is less than 10 mm, the network structure may be sothin that a bottoming feeling is given. The upper limit of the thicknessis preferably not more than 300 mm, more preferably not more than 200mm, still more preferably not more than 120 mm in view of manufacturingequipment.

The 70° C.-compression residual strain of the network structure of thepresent invention is preferably not more than 35%. When the 70°C.-compression residual strain is more than 35%, properties as a networkstructure to be used for an intended cushioning material are notsatisfied.

The 50%-constant displacement repeated compression residual strain ofthe network structure of the present invention is not more than 15%,preferably not more than 10%. When the 50%-constant displacementrepeated compression residual strain is more than 15%, the networkstructure is reduced in thickness after a long period of use, and is notpreferred as a cushioning material. The lower limit of the 50%-constantdisplacement repeated compression residual strain is not particularlydefined, but it is not less than 1% in the case of the network structureobtained in the present invention.

The 50%-compression hardness of the network structure of the presentinvention is preferably not less than 10 N/φ200 and not more than 1000N/ 200. When the 50%-compression hardness is less than 10 N/φ200, abottoming feeling may be given. When the 50%-compression hardness ismore than 1000 N/φ200, the hardness may be so high that cushioningperformance is impaired.

The 25%-compression hardness of the network structure of the presentinvention is preferably not less than 5 N/φ200 and not more than 500N/φ200. When the 25%-compression hardness is less than 0.5 N/φ200, thehardness may be so low that cushioning performance may becomeinsufficient. When the 25%-compression hardness is more than 500 N/φ200,the hardness may be so high that cushioning performance is impaired.

The 50%-compression hardness retention after 50%-constant displacementrepeated compression of the network structure of the present inventionis not less than 85%, preferably not less than 88%, more preferably notless than 90%. When the 50%-compression hardness retention after50%-constant displacement repeated compression is less than 85%, abottoming feeling may be given due to a decrease in hardness of acushioning material with a long period of use. The upper limit of the50%-compression hardness retention after 50%-constant displacementrepeated compression is not particularly defined, but it is not morethan 110% in the case of the network structure obtained in the presentinvention. The reason why the 50%-compression hardness retention mayexceed 100% is that there may be cases where the thickness of thenetwork structure is reduced due to repeated compression, so that theapparent density of the network structure after repeated compression isincreased, leading to an increase in hardness of the network structure.When the hardness is increased due to repeated compression, cushioningperformance is changed, and therefore the 50%-compression hardnessretention is preferably not more than 110%.

The 25%-compression hardness retention after 50%-constant displacementrepeated compression of the network structure of the present inventionis preferably not less than 85%, more preferably not less than 88%,still more preferably not less than 90%, especially preferably not lessthan 93%. When the 25%-compression hardness retention after 50%-constantdisplacement repeated compression is less than 85%, the hardness of acushioning material may be reduced with a long period of use, leading toa change in sitting comfort. The upper limit of the 25%-compressionhardness retention after 50%-constant displacement repeated compressionis not particularly defined, but it is not more than 110% in the networkstructure obtained in the present invention. The reason why the25%-compression hardness retention may exceed 100% is that there may becases where the thickness of the network structure is reduced due torepeated compression, so that the apparent density of the networkstructure after repeated compression is increased, leading to anincrease in hardness of the network structure. When the hardness isincreased due to repeated compression, cushioning performance ischanged, and therefore the 25%-compression hardness retention ispreferably not more than 110%.

The hysteresis loss of the network structure of the present invention ispreferably not more than 28%, more preferably not more than 27%, stillmore preferably not more than 26%, still further more preferably notmore than 25%. When the hysteresis loss is more than 28%, a large forceof repulsion may be hardly felt when a user is seated. The lower limitof the hysteresis loss is not particularly defined, but it is preferablynot less than 1%, more preferably not less than 5% in the case of thenetwork structure obtained in the present invention. When the hysteresisloss is less than 1%, the force of repulsion is so large that cushioningperformance is deteriorated, and therefore the hysteresis loss ispreferably not less than 1%, more preferably not less than 5%.

The number of bonding points per unit weight of a random loop bondedstructure that is the network structure of the present invention ispreferably 60 to 500/g. The bonding point refers to a fused part betweentwo filaments, and the number of bonding points per unit weight (unit:number of points/g) is a value obtained by dividing the number ofbonding points per unit volume (unit: number of points/cm³) in aparallelepiped-shaped piece by an apparent density of the piece (unit:g/cm³), the parallelepiped-shaped piece being prepared by cutting anetwork structure into a parallelepiped shape such that the piece has asize of 5 cm (longitudinal direction)×5 cm (width direction), andincludes two outermost layer surfaces of the sample, but does notinclude the edge of the sample. As a method for measuring the number ofbonding points, the fused part is peeled apart by pulling two filaments,and the number of peelings is counted. In the case of a networkstructure having a belt-like density difference of not less than 0.005g/cm³ in terms of apparent density in the longitudinal direction orwidth direction of the sample, the sample is cut such that a boundaryline between a dense part and a sparse part coincides with anintermediate line in the longitudinal direction or width direction ofthe piece, and the number of bonding points per unit weight is counted.When the number of bonding points per unit weight is in theabove-described range, filaments are moderately restrained, so that anetwork structure is obtained which allows a moderate hardness and forceof repulsion to be easily obtained and gives good sitting or sleepingcomfort. The number of bonding points per unit weight of the networkstructure of the present invention is preferably not less than 60/g andnot more than 500/g, more preferably not less than 80/g and not morethan 450/g, still more preferably not less than 100/g and not more than400/g. When the number of bonding points per unit weight of the networkstructure of the present invention is less than 60/g, the networkstructure may become so coarse that product quality is unsatisfactory,and when the number of bonding points per unit weight is more than500/g, it may become difficult to secure a necessary hardness. In thistext, the bonding point may be described as a contact point.

The network structure of the present invention has such properties thatthe 50%-compression hardness retention after 50%-constant displacementrepeated compression is not less than 85% and the 25%-compressionhardness retention after 50%-constant displacement repeated compressionis not less than 85%. Only when the hardness retention is in theabove-described range, a network structure is obtained which has areduced change in hardness after a long period of use and which can beused for a long period of time with a small change in sitting orsleeping comfort. Previously known network structures having a low50%-constant displacement repeated compressive strain and the networkstructure of the present invention are different in that in the networkstructure of the present invention, fusion of continuous linearstructures that form the network structure is made strong to increasethe strength of contact points between continuous linear structures. Byincreasing the strength of contact points between continuous linearstructures that form the network structure, the hardness retention after50%-constant displacement repeated compression of the network structurecan be improved. That is, in the case of previously known networkstructures, many of contact points between continuous linear structuresthat form the network structure are ruptured due to 50%-constantdisplacement repeated compression, but in the case of the networkstructure of the present invention, rupture of the contact points can bereduced as compared to conventional network structures.

On the other hand, for the 50%-constant displacement repeatedcompressive strain, it is considered that even if contact points of thenetwork structure after repeated compression are ruptured, thecompressive strain is low because the thickness is restored due toelasticity of a polyester-based thermoplastic elastomer that formscontinuous linear structures, and therefore conventional networkstructures have a 50%-constant displacement repeated compressive strainwhich is not much different from that of the network structure of thepresent invention.

The network structure of the present invention has such properties thatthe hysteresis loss is not more than 28%. Only when the hysteresis lossis in the above-described range, a network structure giving sitting orsleeping comfort with a large force of repulsion is obtained. In thenetwork structure of the present invention, fusion of continuous linearstructures that form a network structure is made strong to increase thestrength of contact points between continuous linear structures. Themechanism of increasing the strength of contact points to reduce thehysteresis loss is complicated, and has not been fully cleared, but itcan be presumed as follows. When the strength of contact points betweencontinuous linear structures that form a network structure is increased,rupture of contact points is hard to occur when the network structure iscompressed. Next, when stress is released from the compressed state andthe network structure is restored from the deformed state, the contactpoints are not ruptured but maintained, and therefore restoration fromthe deformed state is accelerated to reduce the hysteresis loss. Thatis, it is considered that in previously known network structures, manyof contact points between continuous linear structures that form anetwork structure are ruptured due to prescribed preliminary compressionor second compression, but in the network structure of the presentinvention, rupture of contact points can be reduced as compared to theconventional network structures, and maintained contact points enablemore effective use of rubber elasticity intrinsic to the polymer to beused.

The network structure of the present invention has such properties thatthe number of bonding points per unit weight is not less than 60/g andnot more than 500/g. When the number of bonding points per unit weightis in the above-described range, a network structure combining qualityand hardness is obtained. The number of bonding points per unit weightcan be adjusted by the heat retaining mold distance, the nozzlesurface-cooling water temperature, the spinning temperature, etc. Amongthem, provision of a heat retaining mold distance is preferred becausethe strength of contact points is increased. It is preferred to adjustthe number of bonding points per unit weight by using one of theabove-mentioned conditions alone or using those conditions incombination.

For example, the network structure of the present invention having ahigh hardness retention after 50%-constant displacement repeatedcompression is obtained in the following manner. The network structureis obtained in accordance with a publicly known method described inJapanese Patent Application No. H7-68061 A etc. For example, apolyester-based thermoplastic elastomer is distributed to nozzleorifices from a multi-row nozzle having a plurality of orifices, anddischarged downward through the nozzle at a spinning temperature higherby not less than 20° C. and less than 120° C. than the melting point ofthe polyester-based thermoplastic elastomer, the continuous linearstructures are mutually contacted in a molten state and thereby fused toform a three-dimensional structure, which is sandwiched by a take-upconveyor net, cooled by cooling water in a cooling bath, then drawn out,and drained or dried to obtain a network structure having both surfacesor one surface smoothed. When only one surface is to be smoothed, thepolyester-based thermoplastic elastomer may be discharged onto aninclined take-up net, and the continuous linear structures may bemutually contacted in a molten state and thereby fused to form athree-dimensional structure, which may be cooled while the form of onlythe take-up net surface is relaxed. The obtained network structure canalso be subjected to annealing treatment. Drying treatment of thenetwork structure may be performed by annealing treatment.

For obtaining the network structure of the present invention, fusion ofcontinuous linear structures of a network structure to be obtainedshould be made strong to increase the strength of contact points betweenthe continuous linear structures. By increasing the strength of contactpoints between continuous linear structures that form the networkstructure, repeated compression durability of the network structure canbe resultantly improved.

As one of means for obtaining a network structure with an increasedstrength of contact points, for example, a heat-retaining region isprovided below a nozzle when a polyester-based thermoplastic elastomeris spun. It is also conceivable that the spinning temperature of thepolyester-based thermoplastic elastomer is increased, but it ispreferred to provide a heat-retaining region below a nozzle from theviewpoint of preventing heat degradation of the polymer. The length ofthe heat-retaining region below a nozzle is preferably not less than 20mm, more preferably not less than 35 mm, still more preferably not lessthan 50 mm. The upper limit of the length of the heat-retaining regionis preferably not more than 70 mm. When the length of the heat-retainingregion is not less than 20 mm, fusion of continuous linear structures ofa network structure to be obtained becomes strong, strength of contactpoints between continuous linear structures is increased, andresultantly repeated compression durability of the network structure canbe improved. When the length of the heat-retaining region is less than20 mm, the strength of contact points is not improved to the extent thatsatisfactory repeated compression durability can be achieved. When thelength of the heat-retaining region is more than 70 mm, surface qualitymay be deteriorated.

For the heat-retaining region, a periphery of a spin pack or an amountof heat carried by the polymer may be used to form a heat-retainingregion, or the temperature of a fiber-falling region immediately below anozzle may be controlled by heating the heat-retaining region with aheater. For the heat-retaining region, a heat-retaining material may beprovided so as to surround the circumference of falling continuouslinear structures below the nozzle by using an iron plate, an aluminumplate, a ceramic plate etc. More preferably, the heat-retaining materialis formed from the above-described materials, and these materials arecovered with a heat-insulating material. As a position where theheat-retaining region is provided, the heat-retaining region ispreferably provided downward from a position of not more than 50 mmbelow the nozzle, more preferably from a position of not more than 20 mmbelow the nozzle, still more preferably from immediately below thenozzle. As one of preferred embodiments, the periphery of an areaimmediately below the nozzle is surrounded by an aluminum plate with alength of 20 mm downward from immediately below the nozzle such that thealuminum plate does not come into contact with a string, therebyretaining heat, and further the aluminum plate is covered with aheat-retaining material.

As another means for obtaining a network structure having an increasedstrength of contact points, the net surface temperature of a take-upconveyor net is increased at or around the falling position ofcontinuous linear structures, or the temperature of cooling water in acooling bath is increased at or around the falling position ofcontinuous linear structures. The surface temperature of the take-upconveyor net is preferably not less than 80° C., more preferably notless than 100° C. For keeping good peeling properties between thecontinuous linear structure and the conveyor net, the conveyor nettemperature is preferably not more than the melting point of thepolymer, more preferably lower by not more than 20° C. than the meltingpoint. The temperature of cooling water is preferably not less than 80°C.

The continuous linear structure that forms the network structure of thepresent invention may be formed as a complex linear structure obtainedby combination with other thermoplastic resins within the bounds of notimpairing the object of the present invention. When the linear structureitself is complexed, examples of the complexed form include complexlinear structures of sheath-core type, side-by-side type and eccentricsheath-core type.

The network structure of the present invention may be formed as amultilayered structure within the bounds of not impairing the object ofthe present invention. Examples of the multilayered structure include astructure in which the surface layer and the back surface layer areformed of linear structures having different finenesses and a structurein which the surface layer and the back surface layer are formed ofstructures having different apparent densities. Examples of the methodfor formation a multilayered structure include methods in which networkstructures are stacked on one after another, and fixed by side groundetc., melted and fixed by heating, bonded with an adhesive, or bound bysewing or a band.

The shape of the cross section of the continuous linear structure thatforms the network structure of the present invention is not particularlylimited, but when the cross section is a solid cross section, a hollowcross section, a round cross section, a modified cross section or acombination thereof, preferred compression resistance and touchcharacteristics can be imparted.

The network structure of the present invention can be processed into amolded article from a resin manufacture process within the bounds of notdeteriorating performance, and treated or processed by addition ofchemicals, etc. to impart functions such as antibacterial deodorization,deodorization, mold prevention, coloring, fragrance, flame resisting,and absorption and desorption of moisture.

The network structure of the present invention thus obtained hasexcellent repeated compression durability with a low repeatedcompression residual strain and a high hardness retention.

Although the present invention will be described in detail withreference to examples, the present invention is in no way limited tothem.

Measurement and evaluation of characteristic value in examples wereperformed by following methods.

(1) Fineness

A specimen was cut into a size of 20 cm×20 cm, and sample was taken from10 places. The linear structures sampled at 10 places were measured fora specific gravity at 40° C. using a density gradient tube. Furthermore,the linear structure sampled at the above-mentioned 10 places wasmeasured for a cross-section area in a photograph magnified by 30 timesunder microscope to calculate a volume for a 10000 m of length of thelinear structure. The product of a specific gravity and the volumeobtained represents fineness (weight for 10000 m of the linearstructure). (Average of n=10)

(2) Sample Thickness and Apparent Density

A sample is cut into a size of 30 cm×30 cm, the cut sample is keptstanding with no load for 24 hours, and then measured for the height at4 points using a thickness gauge Model FD-80N manufactured KOBUNSHIKEIKI CO., LTD., and the average of the measured values is determined asthe sample thickness. The sample weight is measured by placing thesample on an electronic balance. The volume is determined from thesample thickness, and the sample weight is divided by the volume toobtain a value as the apparent density (average of n=4 in each case).

(3) Melting Point (Tm)

An endothermic peak (melting peak) temperature was determined from anendothermic/exothermic curve obtained by measurement at a heating rateof 20° C./min using a differential scanning calorimeter Q200manufactured by TA Instruments.

(4) 70° C.-Compression Residual Strain

A sample is cut into a size of 30 cm×30 cm, and the cut sample ismeasured for a thickness (a) before treatment using the method describedin (2). The sample, whose thickness has been measured, is sandwiched ina tool capable of being held in a 50%-compression state, placed in adryer set at 70° C., and kept standing for 22 hours. Thereafter, thesample is taken out, and cooled to remove a compressive strain, athickness (b) after standing for 1 day is determined, and thecompression residual strain is calculated in accordance with theformula: {(a)−(b)}/(a)×100 from the thickness (b) and the thickness (a)before treatment (unit: %) (average of n=3).

(5) 25%- and 50%-Compression Hardness

A sample is cut into a size of 30 cm×30 cm, and the cut sample is keptstanding under an environment of 20° C.±2° C. with no load for 24 hours,the central part of the sample is then compressed at a speed of 100mm/min with a φ200 mm compression board having a thickness of 3 mm usinga tensilon manufactured by ORIENTEC Co., LTD., which is placed under anenvironment of 20° C.±2° C., and the thickness at a load of 5 N ismeasured as a hardness-meter thickness. The position of the compressionboard at this time is defined as a zero position, and the sample iscompressed to 75% of the hardness-meter thickness at a speed of 100mm/min, followed by returning the compression board to the zero point ata speed of 100 mm/min.

Subsequently, the sample is compressed to 25% and 50% of thehardness-meter thickness at a speed of 100 mm/min, and loads at thistime are measured as a 25%-compression hardness and a 50%-compressionhardness, respectively (unit: N/φ200) (average of n=3).

(6) 50%-Constant Displacement Repeated Compression Residual Strain

A sample is cut into a size of 30 cm×30 cm, and the cut sample ismeasured for a thickness (a) before treatment using the method describedin (2). The sample, whose thickness has been measured, is repeatedlycompressed to a thickness of 509% and restored in a cycle of 1 Hz underan environment of 20° C.±2° C. using Servopulser manufactured byShimadzu Corporation, the sample after 80000 times of repetition is keptstanding for 1 day, followed by determining a thickness (b) aftertreatment, and the 50%-constant displacement repeated compressionresidual strain is calculated in accordance with the formula:{(a)−(b)}/(a)×100 from the thickness (b) and the thickness (a) beforetreatment (unit: %) (average of n=3).

(7) 50%-Compression Hardness Retention after 50%-Constant DisplacementRepeated Compression

A sample is cut into a size of 30 cm×30 cm, and the cut sample ismeasured for the thickness before treatment using the method describedin (2). The sample, whose thickness has been measured, is measured usingthe method described in (5), and the obtained 50%-compression hardnessis defined as a load (a) before treatment. Thereafter, the sample isrepeatedly compressed to 50% of the thickness before treatment andrestored in a cycle of 1 Hz under an environment of 20° C.±2° C. usingServopulser manufactured by Shimadzu Corporation, the sample after 80000times of repetition is kept standing for 30 minutes, and then measuredusing the method described in (5), and the obtained 50% compressionhardness is defined as a load (b) after treatment. The 50%-compressionhardness retention after 50%-constant displacement repeated compressionis calculated in accordance with the formula: (b)/(a)×100 (unit: %)(average of n=3).

(8) 25%-Compression Hardness Retention After 50%-Constant DisplacementRepeated Compression

A sample is cut into a size of 30 cm×30 cm, and the cut sample ismeasured for the thickness before treatment using the method describedin (2). The sample, whose thickness has been measured, is measured usingthe method described in (5), and the obtained 25%-compression hardnessis defined as a load (c) before treatment. Thereafter, the sample isrepeatedly compressed to 50% of the thickness before treatment andrestored in a cycle of 1 Hz under an environment of 20° C.±2° C. usingServopulser manufactured by Shimadzu Corporation, the sample after 80000times of repetition is kept standing for 30 minutes, and then measuredusing the method described in (5), and the obtained 25%-compressionhardness is defined as a load (d) after treatment. The 25%-compressionhardness retention after 50%-constant displacement repeated compressionis calculated in accordance with the formula: (d)/(c)×100 (unit: %)(average of n=3).

(9) Hysteresis Loss

A sample is cut into a size of 30 cm×30 cm, and the cut sample is keptstanding under an environment of 20° C.±2° C. with no load for 24 hours,the central part of the sample is then compressed at a speed of 10mm/min with a φ200 mm compression board having a thickness of 3 mm usinga tensilon manufactured by ORIENTEC Co., LTD., which is placed under anenvironment of 20° C.±2° C., and the thickness at a load of 5 N ismeasured as a hardness-meter thickness. The position of the compressionboard at this time is defined as a zero position, the sample iscompressed to 75% of the hardness-meter thickness at a speed of 100mm/min, and the compression board is returned to the zero position atthe same speed without hold time (first stress strain curve).Subsequently, the sample is compressed to 75% of the hardness-meterthickness at a speed of 100 mm/min without hold time, and thecompression board is returned to the zero position at the same speedwithout hold time (second stress strain curve). The compression energygiven by the second compression stress curve is defined as WC, and thecompression energy given by the second decompression stress curve isdefined as WC′. The hysteresis loss is determined in accordance with thefollowing equation.

Hysteresis loss (%)=(WC−WC′)/WC×100

WC=∫PdT (workload at compression from 0% to 75%)

WC′=∫PdT (workload at decompression from 75% to 0%)

In a simplified manner, the hysteresis loss may be determined by dataanalysis with a personal computer when a stress strain curve as shownin, for example, FIG. 1 is obtained. Further, the area drawn in obliquelines is defined as WC and the area drawn in net-like lines is definedas WC′. Each area of a paper with each curve drawn thereon is cut out tobe measured for a weight, and the target value may be obtained from eachof the weight (average of n=3).

(10) Number of Bonding Points Per Unit Weight

First, a piece was prepared by cutting a sample in a parallelepipedshape such that the piece had a size of 5 cm (longitudinal direction)×5cm (width direction), and included two outermost layer surfaces of thesample, but did not include the edge of the sample. Next, heights at 4corners of the piece were measured, the volume (unit: cm³) was thendetermined, and the weight (unit: g) of the sample was divided by thevolume to calculate the apparent density (unit: g/cm³). Next, the numberof bonding points in the piece was counted, the number was divided bythe volume of the piece to calculate the number of bonding points perunit volume (unit: number/cm³), and the number of bonding points perunit volume was divided by the apparent density to calculate the numberof bonding points per unit weight (unit: number/g). A fused part betweentwo filaments was defined as the bonding point, and the number ofbonding points was counted by a method of peeling apart a fused part bypulling two filaments. The number of bonding points per unit weight wasdetermined as an average of n=2. In the case of a sample having abelt-like density difference of not less than 0.005 g/cm³ in terms ofapparent density in the longitudinal direction or width direction of thesample, the sample was cut such that a boundary line between a densepart and a sparse part coincided with an intermediate line in thelongitudinal direction or width direction of the piece, and the numberof bonding points per unit weight was measured by a similar method(n=2).

EXAMPLES Example 1

As a polyester-based elastomer, dimethyl terephthalate (DMT) and1,4-butanediol (1,4-BD) were charged together with a small amount of acatalyst, transesterification was performed using a usual method,polytetramethylene glycol (PTMG) was then added, and the mixture wassubjected to polycondensation while the temperature was raised and thepressure was reduced, so that a polyether ester block copolymerelastomer was generated. Then, 2% of an antioxidant was added thereto,and the mixture was mixed and kneaded, then pelletized, and dried invacuum at 50° C. for 48 hours to obtain a thermoplastic elastic resinraw material. The formulation of the obtained thermoplastic elasticresin raw material is shown in Table 1.

The obtained thermoplastic elastic resin (A−1) was discharged todownward from a nozzle at a melting temperature of 230° C. and a speedof 2.4 g/min in terms of discharge amount per single hole throughorifices zigzag-arranged at a pitch between holes of 5 mm on a nozzleeffective face of 1050 mm in the width direction and 45 mm in width inthe thickness direction, each orifice shaped to have an outer diameterof 2 mm, an inner diameter of 1.6 mm and have a triple bridge hollowforming cross section. Cooling water of 30° C. was arranged at aposition 28 cm below the nozzle face through a heat-retaining regionprovided immediately below the nozzle with a length of 30 mm. Endlessnets made of stainless steel each having a width of 150 cm were disposedparallel at an interval of 40 mm in opening width to form a pair oftake-up conveyors so as to be partially exposed over a water surface.The conveyor nets over the water surface were not heated with aninfrared heater, and the discharged filaments in a molten state werecurled to form loops on the net having a surface temperature of 40° C.,and contact parts were fused to form a three-dimensional networkstructure. The network in a molten state was sandwiched at both surfacesby the take-up conveyors, and drawn into cooling water at 30° C. at aspeed of 1.2 m per minute, thereby solidified, flattened at bothsurfaces, then cut into a predetermined size, and dried/heat-treatedwith hot air at 110° C. for 15 minutes to obtain a network structure.The properties of the obtained network structure formed of athermoplastic elastic resin are shown in Table 2.

The obtained network was formed of filaments each having a triangularprism-shaped hollow cross section as a cross-sectional shape, and havinga hollowness of 34% and a fineness of 3300 dtex, and had an apparentdensity of 0.038 g/cm³, a thickness of flattened surface of 38 mm, a 70°C.-compression residual strain of 12.2%, a 50%-constant displacementrepeated compression residual strain of 3.3%, a 25%-compression hardnessof 128 N/φ200 mm, a 50%-compression hardness of 241 N/φ200 mm, a50%-compression hardness retention of 90.5% after 50%-constantdisplacement repeated compression, a 25%-compression hardness retentionof 90.8% after 50%-constant displacement repeated compression, ahysteresis loss of 27.2%, and a number of bonding points per unit weightof 134.4/g. The properties of the obtained network structure are shownin Table 2. The obtained network structure satisfied the requirements ofthe present invention, and had excellent repeated compressiondurability.

Example 2

A network structure was obtained in the same manner as in Example 1except that a heat-retaining region was not provided immediately belowthe nozzle, the discharge amount per single hole was 4 g/min, thetake-up speed was 1.5 m/min, the nozzle face-cooling water distance was28 cm, endless nets made of stainless steel having a width of 150 cmwere disposed parallel at an interval of 41 mm in opening width, and thesurfaces of the conveyor nets were heated to 120° C. with an infraredheater. The obtained network structure was formed of filaments eachhaving a triangular prism-shaped hollow cross section as across-sectional shape, and having a hollowness of 35% and a fineness of2800 dtex, and had an apparent density of 0.052 g/cm³, a thickness offlattened surface of 41 mm, a 70° C.-compression residual strain of18.6%, a 50%-constant displacement repeated compression residual strainof 2.9%, a 25%-compression hardness of 220 N/φ200 mm, a 50%-compressionhardness of 433 N/φ200 mm, a 50%-compression hardness retention of 99.6%after 50%-constant displacement repeated compression, a 25%-compressionhardness retention of 92.8% after 50%-constant displacement repeatedcompression, a hysteresis loss of 26.5%, and a number of bonding pointsper unit weight of 322.2/g. The properties of the obtained networkstructure are shown in Table 2. The obtained cushion satisfied therequirements of the present invention, and the obtained networkstructure had excellent repeated compression durability.

Example 3

A network structure was obtained in the same manner as in Example 1except that a heat-retaining region was not provided immediately belowthe nozzle, the spinning temperature was 230° C., the discharge amountper single hole was 2.8 g/min, endless nets made of stainless steelhaving a width of 150 cm were disposed parallel at an interval of 36 mmin opening width, the conveyor nets were not heated, the surfacetemperature thereof was 40° C., and the temperature of cooling water was80° C. The obtained network structure was formed of filaments eachhaving a triangular prism-shaped hollow cross section as across-sectional shape, and having a hollowness of 30% and a fineness of3000 dtex, and had an apparent density of 0.043 g/cm³, a thickness offlattened surface of 35 mm, a 70° C.-compression residual strain of17.9%, a 50%-constant displacement repeated compression residual strainof 4.4%, a 25%-compression hardness of 155 N/φ200 mm, a 50%-compressionhardness of 271 N/φ200 mm, a 50% compression hardness retention of 93.9%after 50%-constant displacement repeated compression, a 25%-compressionhardness retention of 90.3% after 50%-constant displacement repeatedcompression, a hysteresis loss of 27.0%, and a number of bonding pointsper unit weight of 237.5/g. The properties of the obtained networkstructure are shown in Table 2. The obtained cushion satisfied therequirements of the present invention, and the obtained networkstructure had excellent repeated compression durability.

Example 4

A network structure was obtained in the same manner as in Example 1except that a resin A-2 was used as a thermoplastic elastic resin, aheat-retaining region was provided immediately below the nozzle with alength of 30 mm, the spinning temperature was 210° C., the dischargeamount per single hole was 2.5 g/min, the take-up speed was 0.8 m/min,the nozzle face-cooling water distance was 32 cm, the conveyor nets werenot heated, the surface temperature thereof was 40° C., and thetemperature of cooling water was 30° C. The obtained network structurewas formed of filaments each having a triangular prism-shaped hollowcross section as a cross-sectional shape, and having a hollowness of 30%and a fineness of 3200 dtex, and had an apparent density of 0.060 g/cm³,a thickness of flattened surface of 37 mm, a 70° C.-compression residualstrain of 13.1%, a 25%-compression hardness of 61 N/φ200 mm, a50%-compression hardness of 148 N/φ200 mm, a 50%-constant displacementrepeated compression residual strain of 7.4%, a 50%-compression hardnessretention of 102.8% after 50%-constant displacement repeatedcompression, a 25%-compression hardness retention of 93.3% after50%-constant displacement repeated compression, a hysteresis loss of26.1%, and a number of bonding points per unit weight of 164.9/g. Theproperties of the obtained network structure are shown in Table 2. Theobtained cushion satisfied the requirements of the present invention,and the network structure had excellent repeated compression durability.

Example 5

A network structure was obtained in the same manner as in Example 1except that a resin A-3 was used as a thermoplastic elastic resin, aheat-retaining region was provided immediately below the nozzle with alength of 30 mm, the spinning temperature was 210° C., the dischargeamount per single hole was 2.6 g/min, the take-up speed was 0.8 m/min,the nozzle face-cooling water distance was 35 cm, the conveyor nets werenot heated, the surface temperature thereof was 40° C., and thetemperature of cooling water was 30° C. The obtained network structurewas formed of filaments each having a triangular prism-shaped hollowcross section as a cross-sectional shape, and having a hollowness of 30%and a fineness of 2800 dtex, and had an apparent density of 0.061 g/cm³,a thickness of flattened surface of 36 mm, a 70° C.-compression residualstrain of 14.1%, a 25%-compression hardness of 56 N/φ200 mm, a50%-compression hardness of 150 N/φ200 mm, a 50%-constant displacementrepeated compression residual strain of 6.9%, a 50%-compression hardnessretention of 93.8% after 50%-constant displacement repeated compression,a 25% compression hardness retention of 90.0% after 50%-constantdisplacement repeated compression, a hysteresis loss of 22.4%, and anumber of bonding points per unit weight of 361.1/g. The properties ofthe obtained network structure are shown in Table 2. The obtainedcushion satisfied the requirements of the present invention, and thenetwork structure had excellent repeated compression durability.

Example 6

A network structure was obtained in the same manner as in Example 1except that a resin A-1 was used as a thermoplastic elastic resin, aheat-retaining region was provided immediately below the nozzle with alength of 50 mm, the spinning temperature was 210° C., the dischargeamount per single hole was 2.6 g/min, the take-up speed was 1.2 m/min,the nozzle face-cooling water distance was 25 cm, the conveyor nets werenot heated, the surface temperature thereof was 40° C., and thetemperature of cooling water was 30° C. The obtained network structurewas formed of filaments each having a triangular prism-shaped hollowcross section as a cross-sectional shape, and having a hollowness of 30%and a fineness of 3500 dtex, and had an apparent density of 0.041 g/cm³,a thickness of flattened surface of 35 mm, a 70° C.-compression residualstrain of 9.3%, a 25%-compression hardness of 148 N/φ200 mm, a50%-compression hardness of 258 N/φ200 mm, a 50%-constant displacementrepeated compression residual strain of 4.1%, a 50%-compression hardnessretention of 95.3% after 50%-constant displacement repeated compression,a 25% compression hardness retention of 96.4% after 50%-constantdisplacement repeated compression, a hysteresis loss of 27.6%, and anumber of bonding points per unit weight of 87.6/g. The properties ofthe obtained network structure are shown in Table 2. The obtainedcushion satisfied the requirements of the present invention, and thenetwork structure had excellent repeated compression durability.

Comparative Example 1

A network structure was obtained in the same manner as in Example 1except that the resin A-1 was used as a thermoplastic elastic resin, thespinning temperature was 210° C., a heat-retaining region immediatelybelow the nozzle was eliminated, the discharge amount per single holewas 2.6 g/min and the nozzle face-cooling water distance was 30 cm. Theobtained network structure was formed of filaments each having atriangular prism-shaped hollow cross section as a cross-sectional shape,and having a hollowness of 33% and a fineness of 3600 dtex, and had anapparent density of 0.037 g/cm³, a thickness of flattened surface of 40mm, a 70° C.-compression residual strain of 18.9%, a 25%-compressionhardness of 111 N/φ200 mm, a 50%-compression hardness of 228 N/φ200 mm,a 50%-constant displacement repeated compression residual strain of3.2%, a 50% compression hardness retention of 82.9% after 50%-constantdisplacement repeated compression, a 25% compression hardness retentionof 75.7% after 50%-constant displacement repeated compression and ahysteresis loss of 30.4%. The properties of the obtained networkstructure are shown in Table 2. The obtained cushion did not satisfy therequirements of the present invention, and the network structure hadpoor repeated compression durability.

Comparative Example 2

A network structure was obtained in the same manner as in Example 1except that the resin A-2 was used as a thermoplastic elastic resin, thespinning temperature was 200° C., a heat-retaining region immediatelybelow the nozzle was eliminated, the discharge amount per single holewas 2.4 g/min, and the nozzle face-cooling water distance was 34 cm, andthe take-up speed was 0.8 nm/min. The obtained network structure wasformed of filaments each having a triangular prism-shaped hollow crosssection as a cross-sectional shape, and having a hollowness of 34% and afineness of 3000 dtex, and had an apparent density of 0.059 g/cm³, athickness of flattened surface of 38 mm, a 70° C.-compression residualstrain of 16.7%, a 25%-compression hardness of 59 N/φ200 mm, a50%-compression hardness of 144 N/φ200 mm, a 50%-constant displacementrepeated compression residual strain of 8.2%, a 50%-compression hardnessretention of 82.9% after 50%-constant displacement repeated compression,a 25%-compression hardness retention of 84.2% after 50%-constantdisplacement repeated compression and a hysteresis loss of 29.1%. Theproperties of the obtained network structure are shown in Table 2. Theobtained cushion did not satisfy the requirements of the presentinvention, and the network structure had poor repeated compressiondurability.

TABLE 1 Soft segment Number Experi- Hard segment average Melting mentalCom- Grycol Com- molecular Con- point No. ponent component ponent weighttent (° C.) A-1 DMT 1,4-BD PTMG 1000 28 205 A-2 DMT 1,4-BD PTMG 1000 58162 A-3 DMT 1,4-BD PTMG 2000 52 166

TABLE 2 Example Example Example Example Example Example ComparativeComparative 1 2 3 4 5 6 Example 1 Example 2 Thermoplastic Elastic ResinA-1 A-1 A-1 A-2 A-3 A-1 A-1 A-2 Spinning Temperature (° C.) 230 230 230210 210 210 210 200 Heat retaining distance (mm) 30 0 0 30 30 50 0 0Discharge amount 2.4 4 2.8 2.5 2.6 2.6 2.6 2.4 per single hole (g/min)Take-up speed (m/min) 1.2 1.5 1.2 0.8 0.8 1.2 1.2 0.8 Nozzleface-cooling water 28 28 28 32 35 25 30 34 distance(cm) Conveyor netstemperature (° C.) 40 120 40 40 40 40 40 40 Temperature of cooling water(° C.) 30 30 80 30 30 30 30 30 Apparent density (g/cm²) 0.038 0.0520.043 0.060 0.061 0.041 0.037 0.059 Thickness (mm) 36 41 35 37 36 35 4038 Fineness (dtex) 3300 2800 3000 3200 2800 3500 3800 3000 70°C.-compression residual strain 12.2 18.6 17.9 13.1 14.1 9.3 18.9 16.7(%) 50%-constant displacement 3.3 2.9 4.4 7.4 6.9 4.1 3.2 8.2 repeatedcompression residual stain (%) 25%-compression hardness (N/φ 128 220 15561 56 148 111 59 200) 50%-compression hardness (N/φ 241 433 271 148 150258 228 144 200) 50%-compression hardness 90.5 99.6 93.9 102.8 93.8 95.382.9 82.9 retention after 50%-constant displacement repeated compression(%) 25%-compression hardness 90.8 92.8 90.3 93.3 90.0 96.4 75.7 84.2retention after 50%-constant displacement repeated compression (%)Hysteresis loss (%) 27.2 26.5 27.0 26.1 22.4 27.6 30.4 29.1 Number ofbonding points per unit 134.4 322.2 237.5 164.9 361.1 87.6 — — weight(number/g)

INDUSTRIAL APPLICABILITY

The present invention provides a network structure in which durabilityafter repeated compression, which has been not satisfied by conventionalproducts, is improved without deteriorating good sitting comfort and airpermeability which have given heretofore by network structures. Therecan be provided a network structure suitable for cushioning materialsthat are used for office chairs, furniture, sofas, beddings such asbeds, seats for vehicles such as those for trains, automobiles,two-wheeled vehicles, buggies and child seats, and floor mats and matsfor impact absorption such as members for prevention of collision andnipping, etc, the network structure having a small reduction inthickness and a small reduction in hardness after a long period of use.For this reason, the network structure of the present inventionsignificantly contributes to industries.

1. A network structure comprising a three-dimensional random loop bondedstructure obtained by forming random loops with curling treatment of acontinuous linear structure including a polyester-based thermoplasticelastomer and having a fineness of not less than 100 dtex and not morethan 60000 dtex, and by making each loop mutually contact in a moltenstate, wherein the network structure has an apparent density of 0.005g/cm³ to 0.20 g/cm³, a 50%-constant displacement repeated compressionresidual strain of not more than 15%, and a 50%-compression hardnessretention of not less than 85% after 50%-constant displacement repeatedcompression.
 2. The network structure according to claim 1, wherein thenetwork structure has a 25%-compression hardness retention of not lessthan 85% after 50%-constant displacement repeated compression.
 3. Thenetwork structure according to claim 1, wherein the network structurehas a thickness of not less than 10 mm and not more than 300 mm.
 4. Thenetwork structure according to claim 1, wherein the cross section of thecontinuous linear structure that forms the network structure is a hollowcross section and/or a modified cross section.
 5. The network structureaccording to claim 1, wherein the network structure has a hysteresisloss of not more than 28%.
 6. The network structure according to claim1, wherein the network structure has a number of bonding points per unitweight of 60/g to 500/g.
 7. The network structure according to claim 1,wherein the 50%-compression hardness retention is not less than 90%after 50%-constant displacement repeated compression.